1. Field of the Invention
The present invention relates to a Code Division Multiple Access (CDMA) mobile communication terminal, and more particularly, to a device and method of controlling the gain of a Power Amplifying Module (PAM) in a Radio Frequency (RF) transmitter of a mobile communication terminal.
2. Background of the Prior Art
As greater amounts of data are being transmitted as a result of the advances in the technology of network design, and the number of users is greatly increasing in a Code Division Multiple Access (CDMA) mobile communication system, an average transmission power per call is being gradually reduced. Accordingly, an effort is being made to reduce the quiescent power requirements of a transmitter, the power consumption during inactive or non-calling mode, thereby increasing a calling time by reducing battery consumption.
However, due to the chipsetting of parts, only a Power Amplifying Module (PAM) can have its quiescent current reduced. The PAM disposed at an end terminal of a CDMA transmitter mainly uses a gallium arsenide Microwave Monolithic Integrated Circuit (MMIC) to perform its functions. The PAM uses large amounts of quiescent current, and also has a great current saving effect.
An Adjacent Channel Power Ratio (ACPR) of the PAM has a good characteristic at a high gain. The quiescent current of the PAM has less idle current consumed at a low gain.
The gain determined by an input/output value calculation is controlled to obtain appropriate values of the characteristics of the PAM. At power levels ranging from 0 dBm to a maximum power level, the ACPR is more important than the quiescent current, and at power levels below 0 dBm, the quiescent current is important.
Accordingly, depending on a Pulse Density Modulation (PDM) signal of an additional circuit or a modem, the PAM is operated with the high gain at a high output power, and is operated with the low gain at a low output power, or the PAM can be used with an optimal gain fixed.
In other words, the gain of the PAM is controlled where gain is either fixed to provide a good temperature characteristic, or where the gain is reduced at the low output power to reduce the quiescent current.
FIG. 1 illustrates a conventional Power Amplifying Module (PAM) variable gain device.
In FIG. 1, a Power Amplifying Module (PAM) 100 amplifies an output power of an RF transmitter to transmit the amplified power to an antenna terminal. “Pin” denotes an input power input to the PAM 100, and “Pout” denotes an output power amplified through the PAM 100. Accordingly, the output power (Pout) is determined by the input power (Pin) and a gain.
In FIG. 1, the PAM 100 variable gain device has a variable gain. Accordingly, a constant gain is provided to generate a necessary output. A gain control circuit 102 amplifies the input power (Pin) to generate the output power (Pout) according to a predetermined gain.
The PAM 100 is driven by a control signal of an Automatic Gain Controller (AGC) 104 and a Vcontrol output from the gain control circuit 102. A modem 106 drives the AGC 104 and the gain control circuit 102 using a Pulse Density Modulation (PDM) signal, which is a control signal for driving the AGC 104 and the gain control circuit 102.
As described above, in case where an electric field is changed, for example, in case where the electric field is weakened as the communication terminal is moving away from a base station, the PAM 100 requires a high output. At this time, the gain control circuit 102 increases a gain, thereby providing the high output.
FIG. 2 illustrates a conventional PAM fixed gain device.
In FIG. 2, a Power Amplifying Module (PAM) 100 amplifies an output power of a RF transmitter to transmit the amplified power to an antenna terminal. “Pin” denotes an input power input to the PAM 100, and “Pout” denotes an output power amplified through the PAM 100. Accordingly, the output power (Pout) is determined by the input power (Pin) and a gain.
In FIG. 2, the PAM 100 fixed gain device has a preset fixed gain. Accordingly, a necessary output is generated depending on the fixed gain. That is, a fixed gain circuit 103 amplifies the input power (Pin) to generate the output power (Pout) according to a predetermined fixed gain.
The PAM 100 is driven by a control signal of an Automatic Gain Controller (AGC) 104 and a Vcontrol output from the fixed gain circuit 103. A modem 106 drives the AGC 104 using a Pulse Density Modulation (PDM) signal, which is a control signal for driving the AGC 104.
In case where an electric field is weakened as the communication terminal moves away from a base station, the PAM 100 requires a high output. At this time, since the gain is preset, the fixed gain circuit 103 requires a high input power (Pin) to provide the high output. This also causes a high quiescent current.
Meanwhile, the conventional PAM variable gain device providing the variable gain generates a gain deviation of the PAM when it is operated with the low gain.
Especially, the conventional PAM variable gain device creates a high gain deviation to the PAM in the external environment of a temperature of −30 to 60° C., and generates even greater gain deviation at a low power of approximately −50 dBm. Further, if the gain of the PAM is fixed without control, the conventional PAM variable gain device has a constant characteristic in the external environment of the temperature of −30 to 60° C., but has a drawback in that the quiescent current is relatively increased.